Interdecadal change in the relationship between El Nino in the decaying stage and the central China summer precipitation

Year-to-year variations of summer precipitation over the densely populated central China can exert great impacts on the local society and economy. Using the observed and reanalyzed datasets for the period 1960-2020, this study investigates the relationship between the decaying El Nino and the central China summer precipitation (CCSP). The results show that the central China tends to feature excessive precipitation during post-El Nino summers. In particular, we find that such a climatic effect of El Nino exhibits an evident interdecadal strengthening since the early 1990s. This is due to the changing intensity and duration of the El Nino events. Compared to the prior decades (1960-1992), there are stronger intensity and longer duration of the El Nino-related warm sea surface temperature (SST) anomalies in the tropical central Pacific in the epoch after the early 1990s (1993-2020). Through the Walker circulation adjustment, the strengthened intensity and longer duration of the central Pacific SST anomalies cause stronger and longer-lasting easterly anomalies along the equatorial Indian Ocean, which can further intensify the SST warming over the Southwest Indian Ocean (SWIO) in boreal spring following El Nino by forcing a downwelling Rossby wave. The robust SWIO warming induces stronger Indian Ocean basin-wide SST warming and anomalous anticyclone over the Northwest Pacific in post-El Nino summers through initiating a series of ocean-atmospheric interactions. As a result, the anomalous anticyclone would deliver the abundant water vapor to the central China and contribute to increased local summer precipitation. By contrast, in the prior epoch (1960-1992), the El Nino-related SST warming in the central Pacific is relatively weaker and shorter-lasting, which results in weaker Indo-Pacific climate interactions in the decaying summer, thus having no significant impact on the CCSP. Our results highlight a strengthening influence of El Nino on the following summer precipitation over the central China since the early 1990s. This has important implications for the regional seasonal climate prediction.